Field of the Invention
The present invention relates to a thermally conductive sheet that promotes the heat dissipation of a heat-generating electronic part or the like, and a method for producing a thermally conductive sheet. The present application claims priority to Japanese Patent Application No. 2013-128534 filed in Japan on Jun. 19, 2013, which is incorporated into the present application by reference.
Description of the Related Art
With higher performance of electronic equipment, higher density and higher packaging of semiconductor devices have proceeded. With this, it is important to more efficiently dissipate heat generated from electronic parts constituting electronic equipment. A semiconductor is attached to a heat sink such as a heat-dissipating fan or a heat-dissipating plate via a thermally conductive sheet in order to efficiently dissipate heat. As the thermally conductive sheet, sheets of silicone in which a filler such as an inorganic filler is dispersed and contained are widely used.
A further improvement in thermal conductivity is required of such heat-dissipating members, and this is generally addressed by increasing the filling rate of the inorganic filler blended in the matrix for the purpose of high thermal conductivity. But, when the filling rate of the inorganic filler is increased, the flexibility is impaired, and powder falling occurs due to the high filling rate of the inorganic filler. Therefore there is a limit to increasing the filling rate of the inorganic filler.
Examples of the inorganic filler include alumina, aluminum nitride, and aluminum hydroxide. In addition, for the purpose of high thermal conductivity, the matrix may be filled with scaly particles of boron nitride, graphite, or the like, carbon fibers, or the like. This relies on the anisotropy of the thermal conductivity of the scaly particles or the like. For example, in the case of carbon fibers, they have a thermal conductivity of about 600 W/mK to about 1200 W/mK in the fiber direction. In the case of boron nitride, it has a thermal conductivity of about 110 W/mK in the plane direction and a thermal conductivity of the order of about 2 W/mK in the direction perpendicular to the plane direction and is known to have anisotropy.
Japanese Patent Application Laid-Open (JP-A) No. 2006-335957 describes a method of applying a thermally conductive composition containing carbon fibers, and applying a magnetic field to orient the carbon fibers. But, in order that the carbon fibers may be oriented, fluidity is necessary, and therefore in the method described in JP-A No. 2006-335957, the amount of the thermally conductive filler filled cannot be increased.